Read the initial log level from the QUIC_GO_LOG_LEVEL env if present

We deliberately ignore any parsing errors.

Fixes #501.

utils/log.go

@@ -4,15 +4,16 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strconv"
 	"sync"
 )
 
-var out io.Writer = os.Stdout
-
 // LogLevel of quic-go
 type LogLevel uint8
 
 const (
+	logEnv = "QUIC_GO_LOG_LEVEL"
+
 	// LogLevelDebug enables debug logs (e.g. packet contents)
 	LogLevelDebug LogLevel = iota
 	// LogLevelInfo enables info logs (e.g. packets)
@@ -23,9 +24,12 @@ const (
 	LogLevelNothing
 )
 
-var logLevel = LogLevelNothing
+var (
+	logLevel           = LogLevelNothing
+	out      io.Writer = os.Stdout
 
-var mutex sync.Mutex
+	mutex sync.Mutex
+)
 
 // SetLogWriter sets the log writer.
 func SetLogWriter(w io.Writer) {
@@ -68,3 +72,19 @@ func Errorf(format string, args ...interface{}) {
 func Debug() bool {
 	return logLevel == LogLevelDebug
 }
+
+func init() {
+	readLoggingEnv()
+}
+
+func readLoggingEnv() {
+	env := os.Getenv(logEnv)
+	if env == "" {
+		return
+	}
+	level, err := strconv.Atoi(env)
+	if err != nil {
+		return
+	}
+	logLevel = LogLevel(level)
+}

utils/log_test.go

@@ -60,4 +60,21 @@ var _ = Describe("Log", func() {
 		SetLogLevel(LogLevelDebug)
 		Expect(Debug()).To(BeTrue())
 	})
+
+	It("reads log level from env", func() {
+		Expect(logLevel).To(Equal(LogLevelNothing))
+		os.Setenv(logEnv, "1")
+		readLoggingEnv()
+		Expect(logLevel).To(Equal(LogLevelDebug))
+	})
+
+	It("does not error reading invalid log levels from env", func() {
+		Expect(logLevel).To(Equal(LogLevelNothing))
+		os.Setenv(logEnv, "")
+		readLoggingEnv()
+		Expect(logLevel).To(Equal(LogLevelNothing))
+		os.Setenv(logEnv, "asdf")
+		readLoggingEnv()
+		Expect(logLevel).To(Equal(LogLevelNothing))
+	})
 })